Represents the ratio in which the excess development costs will be split under the license and collaboration agreement.

No definition available.

Name:	lci_LicenseAndCollaborationAgreementExcessDevelopmentCostSplitRatio
Namespace Prefix:	lci_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the period for which profit is split in a specified ratio under the license and collaboration agreement.

+ References

No definition available.

+ Details

Name:	lci_LicenseAndCollaborationAgreementProfitSplitPeriod
Namespace Prefix:	lci_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the ratio in which the profit will be split under the license and collaboration agreement.

+ References

No definition available.

+ Details

Name:	lci_LicenseAndCollaborationAgreementProfitSplitRatio
Namespace Prefix:	lci_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

The fixed interest rate on a loan receivable.

+ References

No definition available.

+ Details

Name:	lci_LoansReceivableFixedRate
Namespace Prefix:	lci_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Minimum amount to be considered for conversion of loan to ownership interest.

+ References

No definition available.

+ Details

Name:	lci_MinimumAmountToBeConsideredForConversionOfLoanToOwnershipInterest
Namespace Prefix:	lci_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of employees of the company who are the members in the board of the entity.

+ References

No definition available.

+ Details

Name:	lci_NumberOfEmployeesInMembersOfBoardOfEntity
Namespace Prefix:	lci_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of members comprised in the board of the entity.

+ References

No definition available.

+ Details

Name:	lci_NumberOfMembersInBoardOfEntity
Namespace Prefix:	lci_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Ownership interest for conversion under agreement advances receivable, contractual obligations.

+ References

No definition available.

+ Details

Name:	lci_OwnershipInterestForConversionUnderAgreement
Namespace Prefix:	lci_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage of outstanding loan sold to third party.

+ References

No definition available.

+ Details

Name:	lci_PercentageOfOutstandingLoanSoldToThirdParty
Namespace Prefix:	lci_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The expiration period of agreement with VIE.

+ References

No definition available.

+ Details

Name:	lci_VariableInterestEntityExpirationPeriod
Namespace Prefix:	lci_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

For an unclassified balance sheet, reflects the carrying amount of unpaid loan amounts due from related parties at the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(e))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_LoansAndLeasesReceivableRelatedParties
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

+ References

No definition available.

+ Details

Name:	us-gaap_OtherCommitment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_OtherCommitmentsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash inflow associated with the sale of loans receivables arising from the financing of goods and services.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3179-108585

+ Details

Name:	us-gaap_ProceedsFromSaleOfLoansReceivable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_OtherCommitmentsAxis=lci_LicenseAndCollaborationAgreementWithHecMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementScenarioAxis=lci_LicenseAndCollaborationAgreementCommercializationFirstTenYearsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementScenarioAxis=lci_LicenseAndCollaborationAgreementFiveYearsAfterFirstTenYearsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Commitments - Other Commitment (Details) $ in Millions	3 Months Ended
Commitments - Other Commitment (Details) $ in Millions	Dec. 31, 2019 USD ($)	Sep. 30, 2018 USD ($)	Mar. 31, 2017 USD ($) item employee
License and Collaboration Agreement With HEC
Commitments
Maximum amount to be loaned	$ 32.0
License and Collaboration Agreement, Excess Development Cost Split Ratio	1
Other Commitment	$ 32.0
License and Collaboration Agreement With HEC \| First ten years
Commitments
License and Collaboration Agreement, Profit Split Ratio	1
License and Collaboration Agreement, Profit Split Period	10 years
License and Collaboration Agreement With HEC \| Next five years
Commitments
License and Collaboration Agreement, Profit Split Ratio	1.5
License and Collaboration Agreement, Profit Split Period	5 years
Variable interest entity
Commitments
Maximum amount to be loaned			$ 15.0
Expiration period			7 years
Loans receivable fixed rate (as a percent)			2.00%
Minimum amount to be considered for conversion of loan to ownership interest			$ 7.5
Ownership interest for conversion (in percentage)			50.00%
Members in the board of the entity \| item			5
Lannett employees as members of the board of the entity \| employee			1
Percentage of outstanding loan		50.00%
Proceeds from sale of loan		$ 5.6
Loan receivable	$ 6.4
Other Commitment			$ 15.0